What common mechanical device did Leonardo da Vinci sketch using rolling balls?

Leonardo da Vinci sketched a ball bearing using rolling balls.

In the late 15th century, Leonardo drew a mechanism in which balls moved between rings. The arrangement was intended to reduce friction by replacing sliding contact with rolling contact, the central principle behind ball bearings.

Leonardo is often credited with the earliest known design for a ball bearing, although he did not invent every form of rolling bearing. Earlier civilizations used rollers and related ideas, and practical bearing development continued long after Leonardo’s sketches.

Modern ball bearings place hardened balls between inner and outer races. These components reduce friction and help support rotating shafts in machines, vehicles, and appliances. Leonardo’s drawing is historically important because it clearly explores the same basic arrangement, but it should not be confused with a modern mass-produced bearing.